Disc brake system with abs

ABSTRACT

An ABS brake system employs two axially slidable brake discs and four brake pads that are biased to have floating light random contact therebetween in the off brake position. The ABS controller operates the brake pads with about one half of the usual brake pressure and about double the number of the usual braking and release cycles. The floating axially slidable brake discs and four brake pads have reduced residual torque drag during the brake release cycle and have reduced hystersis. The result is operation at a higher frequency and with less amplitude, than the usual sliding caliper and fixed brake system, and a resolution of a modulating scale for cycling that is usually associated with a much lower coefficient of friction surface than is actually present.

[0001] This application is a Continuation-In-Part of U.S. patentapplication Ser. No. 09/303,183, entitled “Slidable Brake Disc System”,filed Apr. 30, 1999, and this application is a Continuation-In-Part ofPCT application, Application No. PCT/GB97/03388, filed Dec. 8, 1997,designating the United States and a Continuation-In-Part of PCTapplication, Application No. PCT/GB97/03386 filed Dec. 8, 1997,designating the United States. PCT applications PCT/GB97/03388 andPCT/GB97/03386 are hereby incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

[0002] This invention relates to an ABS braking system for motorvehicles.

BACKGROUND OF THE INVENTION

[0003] Typically, production vehicles, such as automobiles having aAutomatic Braking System (ABS) employ a single brake disc fixed to thewheel hub and a sliding brake caliper mounted on a suspension member ofthe vehicle. Operation of a brake foot pedal by the operator withexcessive force is sensed by a sensor, and a deceleration of the wheelis sensed by a wheel position or speed sensor mounted adjacent thewheel. The wheel speed sensor particularly monitors for front wheellocking up while in the braking condition with its loss of steerabilityand its longer stopping distance. The stopping distance of the vehiclemay be made shorter if the wheels are operated iteratively at a low sliprather than a longer, fully locked or skid condition. The brake caliperis preferably operated at a high brake torque “apply” rate to increasebrake torque for quick response. Additionally, caliper preferably isoperated at a “high release” rate to decrease brake torque for quickresponse when the condition of lock-up is sensed as about to begin toallow the wheel to accelerate to a velocity approaching the vehiclevelocity.

[0004] In conventional production vehicles having this fixed brake discand slidable brake caliper, a hydraulic piston in a hydraulic cylinderon the caliper is operated to shift an inner movable brake pad intobraking engagement with one side of the brake disc fixed to a rotatingwheel hub mounted on the vehicle suspension. A reaction force from thehydraulic fluid moving the piston shifts the slidable caliper to slidethe caliper and a second brake pad on the distal end of a caliper intoengagement with the other side of the fixed brake disc. Typically, thebraking system operates with hydraulic fluid at a pressure of about 70BAR or more to provide the clamping pressure to opposite sides of thebrake disc.

[0005] From the foregoing, it will be understood that when highexcessive force is applied to a brake pedal by a vehicle operatorcausing rapidly deceleration of the wheel towards the lock-up condition,the ABS sensors and control system senses the rotational position of thewheel relative to the vehicle's speed; and if these conditions arewithin preset stored parameters, the ABS hydraulic system is activatedto operate the brakes. The ABS hydraulic system isolates thepedal-operated hydraulics, and the braking operation is taken over bythe ABS system, which causes the braking effort to drop and allows thewheel rotation to accelerate or spin up. When the wheel spin-upapproaches the vehicle speed, as sensed by the wheel sensor, but doesnot equal the vehicle speed, the ABS hydraulics apply increasedhydraulic pressure to the sliding caliper to decrease or spin down thebraked wheel's rotational velocity. When the vehicle wheel spins down toapproach vehicle lock as sensed by the wheel sensor and within thepreset parameters, the ABS hydraulic pressure at the slidable caliper isincreased to allow wheel spin up. This process is iterated to providemodulation of the ABS hydraulic pressure and a deceleration of thevehicle's velocity to provide a stopping of the vehicle within apredetermined distance depending on the kind of surface on which thewheels are engaging. Manifestly, the stopping distance on ice or otherlow coefficient of friction surfaces is greater than the slopingdistance for higher coefficient of friction surfaces. Governmentalregulations in many countries require the ABS braking system to stop thevehicle within a set stopping distance for a given coefficient offriction surface.

[0006] The ABS system senses the initial apply rate and release ratesand scales or calibrates the resolution of subsequent “apply” and“release” rates to stop the vehicle. For example, the amplitude of theinitial apply and release rates is quite high when the wheel is on a dryconcrete surface and the frequency of the brake applications andreleases is quite large in amplitude and at a low frequency. The ABSsystem then compares the frequency and amplitude of brake apply andbrake release rates relative to the preset stored parameters in acontroller and then operates the braking system according to thisalgorithm that is used to decelerate the vehicle's speed to stop thevehicle with the governmental stopping distance. This deceleration isusually a constant deceleration and is linear with respect to time andvehicle velocity or distance traveled. Hereinafter, this will be calleda vehicle deceleration curve, which need not be linear, but which isusually a linear curve. A graphical representation of vehicle wheelspeed and of hydraulic pressure shows that they are modulated along thistheoretical vehicle deceleration curve until the vehicle is slowed downto a very low speed, e.g., under 10 mph when the brakes are allowed tolock up to complete the stopping of the vehicle. If the same vehicletraveling at the same speed and braked with the same brake pedalpressure was traveling on polished ice, having a very low coefficient offriction, relative to the coefficient of friction for the concretesurface, the initial braking by the ABS system recognizes this and setsthe scale or calibration to generate a finer resolution with a morefrequent application and release of the brakes and with a smalleramplitude of wheel acceleration and deceleration. Thus, with a smallercoefficient of friction surface, the average pressure variation andwheel acceleration is less over the stopping distance.

[0007] Current ABS braking systems suffer from being relatively heavy inweight, in being relatively costly, and from operational deficienciessuch as operating at high pressures, high residual torque drag, andlarge hystersis losses. The present invention is directed to providing asignificant weight reduction, for example, with respect to onecommercial automobile, to reduce the weight of the braking system fromabout 18 kilograms to 15 kilograms of unsprung weight at the wheel. Acost saving of thirty (30%) percent or more can be achieved relative tothe braking system currently used on a commercial vehicle. As will beexplained in detail hereinafter, better operation is achieved with areduction in residual torque drag, which occurs when the brake pads rubagainst the brake disc when the brake pedal has not been operated. Areduction in residual torque drag results in a significant increase inbrake pad life, lower operating temperatures, and faster wheelacceleration as will be described in more detail hereinafter.

[0008] To facilitate acceptance and adoption of the braking system ofthis invention by original equipment manufacturers, the preferredbraking system of this invention may be used with the same installed ABScontroller and operating system on vehicles now in use. The preferredbraking system without the ABS control system is more fully described inthe aforesaid copending United States patent application and to a lesserextent hereinafter in this application. This braking system includestwin slidable brake discs and four brake pads for rubbing or clampingengagement with the four sides on the twin brake discs and a fixedcaliper mounted on a suspension stub axle or knuckle. Preferably, thehydraulic cylinder for operating the brake discs is formed integrallywith the suspension knuckle; and an outer, distal brake pad is fixedlymounted on a stationary bridge of the caliper. This is unlike thecurrent slidable caliper on the typical conventional disc brake that hasonly two rubbing surfaces engaging opposite sides of a cast iron or castaluminum, heavy brake rotor.

[0009] The present invention is, as stated above, directed to providinga better ABS system from an operational standpoint. Current ABS systemssuffer from a number of shortcomings. One of these shortcomings is thatthey operate at relatively high hydraulic pressures, for example, 70 BARon high friction surfaces. With only two braking surfaces for a wheel, alarge amount of energy must be dissipated at each rubbing surface todecelerate the vehicle quickly. These high brake pressures result inlarge amplitude variations in hydraulic pressure when the brakes arebeing applied and released. During the long period of time that thebrake pressure is released to allow wheel acceleration toward thevehicle's velocity, the vehicle is moving forwardly with no brakingeffort being applied to decelerate the vehicle.

[0010] With a finer resolution of the frequency and amplitude about atheoretical, vehicle braking curve, the time for an individual cycle ofbrake application and brake release is much quicker so that many more ofthese cycles are performed in the same period of time than for a higherresolution braking system. Hence, it would be desirable to have an ABSsystem with increased resolution more closely approximating thevehicle's deceleration curve. Another factor involved in the obtainingof better braking and, also in obtaining finer resolution of braking andreleasing cycles is that of the hystersis of the system, which involveswasted energy and time put into the system. For example, in the currenthydraulic systems there are expandable, flexible, hydraulic hoses orlines that expand during the high pressure braking and contract duringthe lower pressure release of the brakes. Also, several seals areexpanded during high pressure braking and then contract during thepressure release. One such seal in a hydraulic braking system is theannular seal about the piston of the brake caliper's cylinder. This sealis expanded during braking and contracts during brake release and exertsa return force to return the piston.

[0011] Another operational shortcoming of the commonly used slidablecaliper, single disc braking system is the amount of deflection of thedistal brake pad's support at an outer end of the caliper. That is, inthe current disc braking system, the large, heavy sliding caliper has afixed pad on the caliper which is that outer end of a caliper bridge.This caliper and its bridge are large and heavy because they carry thepiston and the outer distal pad and provide the stiffness needed toresist bending and deflection from the large clamping forces beingapplied. Despite its being relatively heavy and large, the caliper'sdistal end often deflects about 0.0006 inch or greater. The operation inthe system is affected by this deflection of the caliper's distal endand the time needed to slide the heavy caliper back to its brake releaseposition.

[0012] As stated above, the operational performance of an ABS disc brakesystem is adversely affected by residual drag of the brakes when thebraking pressure has been released. Residual braking torque retardswheel spin up to the desired speed, and thus, slows the time ofresponse. It has been found that the conventional slidable caliper brakedisc herein described has significant residual torque or brake drag. Onecause may be that the brake disc is fixed to a stub and whatevertolerance it has from a true perpendicular relationship to therotational axes of the wheel results in rubbing of the disc at highspots, which is called “run out”. That is, the fixed disc or rotor willnot run absolutely true because you have manufacturing tolerances in itssupport including bearings, hubs or axles, and in the disc itself, whichis cast with angular portion therein. This rotating fixed rotor has ageometry envelope within which its annular braking surface travelsduring a wheel revolution. When a high spot on the rotor hits or rubsagainst a brake pad, it pushes against the high mass, caliper, andresidual torque drag is the result. This reduces the life of brake padsand wastes fuel and energy. Also, as the wheel is released by the ABSsystem to accelerate toward the vehicle velocity, the wheel mustovercome this residual torque drag as it accelerates. This residualtorque drag prolongs the time needed to reach the desired wheel velocityand thus, increases the stopping distance for the ABS braking system.That is, the higher hydraulic operating pressures and mass of thesliding caliper and associated friction losses of this sliding calipersystem result in more time betweens spin down and spin up. Hence, itwould be desirable to provide a more effective ADS system wherein thefrequency of spin up and spin down is faster.

[0013] To provide an effective ABS braking system, the brake systemitself must pass rigorous specifications for wear, vibration, residualtorque as well as various road tests for brake fade, for temperature ofoperation on mountainous descents or curvy roads over long period oftime, etc. Some of the current brake systems using two brake pads and asingle fixed brake disc operate at such high temperatures they eitherfail or are having difficulty in passing the Auto Motive Standard (AMS)road test.

[0014] Additionally, for a brake system to be installed on productionvehicles, it must operate successfully and be free of vibrations, noiseor other adverse feel conditions that are deemed undesirable by thevehicle operator. Of course, longevity of the brake pads and discs witha minimum of wear at localized areas that results in disc thicknessvariation (DTV) is most desirable to avoid vibrations and replacement ofbrake discs and/or brake pads. In an off-brake condition, the brake padsand brake disc can touch, particularly when cornering or traveling overbumpy surfaces and cause residual torque drag. This residual torque dragis additional to that above-described due to manufacturing tolerances.

SUMMARY OF THE INVENTION

[0015] In accordance with the present invention, there is provided a newand improved ABS braking system for vehicles that is lighter in weight,lower in cost and has improved operating characteristics. To achievethese ends, the preferred ABS system is formed with a pair of slidable,thin brake discs, which are mounted in a floating manner on a wheel huband this floating allows the brake discs to position themselves quicklyand with reduced, residual brake torque. From a weight standpoint, thesebrake discs are thin, flat plates made of steel, aluminum or a compositematerial as contrasted to the heavy cast, angular rotors currently used.The hydraulic brake cylinder is integrally formed inside the stub axleor knuckle to provide a significant weight savings. From an operationalstandpoint, the ABS system works at substantially reduced hydraulicpressures and has a higher frequency of wheel deceleration andaccelerations, and lower amplitude of pressure and wheel velocities thanthat of the conventional ABS system. Thus, there is provided an ABSbraking system operating at a lower pressure, with reduced hystersis,and improved modulation of braking relative to a conventional,production ABS system which was a slidable caliper and a pair of brakepads cooperable with a single, fixed brake disc.

[0016] This is achieved by employing with the ABS electronic controllersystems a braking system using four rubbing or braking surfaces and twoslidable discs, a lighter and smaller caliper, greater caliperstiffness, reduced hystersis and lower operating forces.

[0017] In accordance with the invention, the preferred ABS brakingsystem, when used on a conventional vehicle having a standard ABScontroller, develops from the initial application of the brakingapplication a resolution of modulating scale for cycling that isassociated with a much lower coefficient of friction surfaces than isactually present. That is, the same ABS controller on a high coefficientof friction road surfaces operates the conventional, fixed, single brakedisc system in the manner associated with this high coefficient offriction surface but operates the twin, slidable brake disc system inthe manner associated with a much lower coefficient of friction, roadsurface. This is a result of using the slidable pair of brake discs andfour brake pads operating at about one half of the usual hydraulicpressure and having reduced residual torque drag and hystersis such thatthe initial cycles used to scale or calibrate the modulators is one halfor less than that used for the conventional sliding caliper and fixeddisc kind of system. Stated differently, when using a conventional ABSsystem controller and hydraulic master cylinder system connected to thepreferred turn, slidable base discs and four brake pads, the system willprovide more than double the number of braking and release cycles perunit time. The braking and release cycles will have a much higherfrequency and a substantial less amplitude meaning that the vehicle willbe decelerating more closely to the desired vehicle deceleration curveset by the ABS controller.

[0018] In accordance with an important aspect of the invention, theslidable brake pads are mounted upwardly at about a 12:00 o'clockposition with a wheel speed, pulse generator located adjacent thereto soas not to interfere with the locking angle and turning circle of thevehicle suspension. Preferably, the hydraulic cylinder is integrallyformed at the top of the suspension member. Also, it is preferred toprovide the seal ring between the piston and the cylindrical wall of thecylinder with a low friction surface, such as a Teflon surface, toreduce hystersis.

[0019] In the preferred embodiment, the wheel speed pulse generatorincludes an annular air cooling ring attached to the rotatable hub withequally spaced tabs arranged in a circle concentric with the wheel axle.A magnetic sensor is mounted on the suspension member adjacent the fixedcaliper to sense the spaced tabs and thereby, the rotational speed ofthe wheel relative to lock-up and/or vehicle speed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1A is a diagrammatic view of a twin braking ABS systemembodying the invention;

[0021]FIG. 1B is a graph showing operational characteristics of the ABSbraking system of FIG. 1A applied to an automobile and embodying theinvention;

[0022]FIG. 1C is a graph showing operational characteristics of aconventional ABS braking system on the same vehicle used for FIG. 1A;

[0023]FIG. 1D illustrates a pressure reduction by about one-half and anabout doubling of frequency of brake application and release between thetwin ABS system of this invention and the conventional ABS system;

[0024]FIG. 1E illustrates a reservoir of hydraulic fluid mounted andhydraulic control valve mounted on a vehicle wheel suspension andoperable in accordance with the invention;

[0025]FIG. 1F illustrates a solenoid force actuator mounted in a hollowbore of a stub axle of the suspension; and

[0026]FIG. 1G illustrates an ABS system for operating the preferred twindisc brake assembly;

[0027]FIG. 2 is a diagrammatic view of an outer spring constraining thebrake pads and an inner spring constraining the brake discs;

[0028]FIG. 3 is a plan view showing the spring constraining the brakepads;

[0029]FIG. 3A is a cross-sectional view showing the spring applyingrestraining forces to the tops of the brake pad carriers;

[0030]FIG. 4 is a diagrammatic view of three leaf spring constraining abrake disc on a hub;

[0031]FIG. 5 is an exploded view of the illustrative assembly;

[0032]FIG. 6 is a side elevational view of the illustrative assembly;

[0033]FIG. 7 is similar to FIG. 6 but shows the illustrative assembly invertical cross section;

[0034]FIG. 8 shows temperature decay curves for disc brakes due toresidual drag torque with the brakes off;

[0035]FIG. 9 shows curves for an AMS fade test of a standard fixedbrake;

[0036]FIG. 10 shows the curves for an AMS fade test of a twin discbrake;

[0037]FIG. 11 is a vertical cross-sectional view taken through asuspension link of the illustrative assembly;

[0038]FIG. 12 is a view similar to FIG. 16, but of a modification of theillustrative assembly;

[0039]FIG. 13 is a perspective view of an alternative leaf spring havingraised ribs thereon;

[0040]FIG. 14 is a diagrammatic, enlarged view of the points of contactbetween the leaf springs and the brake disc;

[0041]FIG. 15 is an enlarged, fragmentary and exploded view of thedriving connection between a hub and slidable brake disc;

[0042]FIG. 15A is similar to FIG. 15 except that the driving connectionis enlarged and meshed to drive the brake disc with rotation of the hub;

[0043]FIG. 16 is a view taken in the direction of the arrow XVI in FIG.6;

[0044]FIG. 17 is a view taken in the direction of the arrow XVII in FIG.7; and

[0045]FIG. 18 is a view showing two solenoids to operate the brake padcarriers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0046] As shown in the drawings for purposes of illustration, theinvention is embodied in an ABS braking system 9 (FIG. 1A) having anelectronic control unit 11 controlling a hydraulic system connected to aforce actuator 13 which supplies the actuating force used to operate abraking disc assembly 10 having a pair of brake discs 38 and 40 whichare braked decelerated by clamping forces from four braking pads 50, 54,56 and 60 (FIG. 1G). The illustrated braking assembly will be describedin connection with the illustrated embodiment of the invention whereinthe braking system is for a front wheel (not shown) of a frontwheel-drive car. The ABS controlled braking system of this invention maybe applied to any vehicle whether front or rear wheel drive and to therear wheel brakes as well as the front wheel brakes.

[0047] The ABS braking system 9 of this invention employed the slidablepair of brake discs 38 and 40 and the cooperating four braking pads 50,54, 56 and 60 and employed a conventional ECU 11 provided on aproduction automobile. The braking system was tested on variouscombinations of road surfaces including, but not limited to, roadsurfaces with a very low coefficient of friction, such as polished ice,as well as normal dry road surfaces and combinations thereof. An ABScontroller 15 develops a theoretical vehicle reference speed which isdepicted herein as a substantially linear deceleration curve 99 (FIGS.1B and 1C) for the stopping distance depending upon a number of factorsincluding the vehicle's velocity and the coefficient of friction for thesurface engaging a wheel or wheels. Typically, each wheel is separatelycontrolled as one or the other of the wheels made by a lower efficientsurface such as ice while another wheel may be on dry pavement with ahigh coefficient of friction. In the example illustrated in FIG. 1B forthe twin braking disc assembly of this invention, the vehicle wastraveling at 80 kilometers per hour and then the brakes were appliedvery hard. The vehicle's wheel speed is sensed during the decelerationof the vehicle and is depicted in FIGS. 1B and 1C, as anacceleration/deceleration curve 100. This wheel speedacceleration/deceleration curve 100 has alternating wheel decelerationportions 100 a and wheel acceleration portions 100 b. Thus, will be seenfrom curves 100 on FIGS. 1B and 1C that the ABS control system appliesbrake shoes against the brake discs and releases the braking forceiteratively to decelerate the wheel and then to release the brakes toallow the wheel to accelerate towards the vehicle velocity. Herein, thecurve 100 is substantively linear from an upper left end 99 a where thevehicle is traveling at 80 kph until it is stopped at a lower right endportion 99 b on the curve 99. The horizontal axis of the graph is intime based units that can be with the vehicle having been stopped afterso many units of travel time.

[0048] Thus, the wheel acceleration/deceleration curves 100 each showthe wheel being decelerated along the downward sloping portion 100 awhen the brakes are applied and an ascending portion 100 b, as the wheelbrakes are released and the wheel is allowed to acceleration toward thevehicle velocity, which is slightly less than the vehicle referencespeed, as shown by the curve 99 immediately thereabove. A brake applyand release cycle generates a deceleration beginning at a higher wheelvelocity 100 a and continuing to the lowest wheel 100 d and then thecurve shows the wheel velocity rising along curve portion 100 b toanother maximum wheel velocity 100 c to initiate the brake apply andrelease cycle.

[0049] The graph of FIG. 1C was generated during the braking of aproduction vehicle employing the single fixed disc or rotor and aslidable caliper (not shown) having a pair of brake discs. Similarreference characters have been used on the curves of FIGS. 1B and 1C todesignate the same things such as deceleration, acceleration, vehiclevelocity, pressure of hydraulic fluid and the time or distance traveled.The conventional sliding caliper and single brake rotor on the testvehicle were replaced with the braking assembly having the twin discsand four braking pads illustrated here. The same ABS controller systemwas used to operate the conventional braking system as well as the twindisc braking system illustrated and described herein. The curves ofFIGS. 1B and 1C were generated for a pair of front wheels on a lowcoefficient of friction surface, viz. polished ice. Other data weregenerated for high friction surfaces and a combination of low and highfriction surfaces.

[0050] Brake fluid pressure curves 102 are also provided in FIGS. 1B and1C to show the hydraulic pressure during each brake apply and releasecycle. The downwardly sloping portion 102 a shows a dropping fluidpressure as the brakes are released and shows an ascending fluidpressure portion 102 b as the brakes are applied. For each iterativebrake apply and release cycle the fluid pressure descends as the wheelaccelerates toward vehicle speed and then the fluid pressure ascends asthe wheel is decelerated toward the wheel locking condition. An averagefluid brake pressure line 104 is also shown in FIGS. 1B and 1C. Thebrake pressure is modulated as by a hydraulic modulating valve 17 (FIG.1A). When the wheel deceleration exceeds the vehicle deceleration by adefined amount the ECU 11 signals the pressure modulating valve tomodulate and reduce the line pressure. When the wheel accelerates and ata defined point, the ECU 11 signals the modulating valve 17 to restoreline pressure.

[0051] In accordance with the present invention, there is provided anABS braking system having a finer resolution or frequency of brakesapply and release cycles and with the cycles being of less amplitude forwheel acceleration/deceleration. Additionally, the present inventionprovides a reduction in fluid pressure by about one-half, as can be seenfrom a comparison of the average fluid pressure curves 103 of FIGS. 1B,1C and 1D, which is desirable from a hystersis standpoint where theexpansion and contraction of seals and expandable fluid hoses takes timeand energy. While the same amount of energy is needed to stop thevehicle, more energy and time is wasted due to hystersis. In addition toa substantial reduction in pressure, it can be seen from a comparison ofthe respective pressure cycles, as depicted in FIG. 1D, that theamplitude of pressure changes is substantially smaller for the ABS twinbrake system than for the amplitude of pressure changes for theconventional braking system. Additionally, the fluid pressure cycles aremore frequent for the twin brake ABS system than for the conventionalABS system, as depicted in FIG. 1D.

[0052] As will be explained in greater detail hereinafter, in the twinbrake ABS system, the wheel accelerates faster towards vehicle speedduring wheel spin-up portion 100 b because of a significantly lessresidual torque drag from the twin disc and four brake system 10 ascompared to the conventional single, fixed rotor and slidable caliper.This residual brake drag is present during the wheel spin-up while thebrake is in the release mode to retard the wheel acceleration.

[0053] From weight and cost standpoints, it is preferred to provide anintegral hydraulic cylinder 72 (FIG. 5) formed in the stub axle 12 witha piston 14 therein; thin slidable flat brake discs 38 and 40 of steel;and a smaller fixed caliper carrying the brake pads 50, 54, 56 and 60.Significant weight reductions for example from about 18 kilograms to 15kilograms has been achieved in this example. Further cost and weightsavings are achievable by using lighter weight and/or smaller seals andhoses because the reduction of about 50% in the operating pressurebetween the two ABS systems (FIGS. 2 and 3). A reduction of 3 kilogramsor more of unsprung weight at the wheels which transmit vibrations,noise and harshness back into the vehicle is an important andsignificant contribution. Thus, it will be seen that the presentinvention provides an ABS system which is lower in cost, lighter inweight, and operates more efficiently than the conventional ABS systemto which it is being compared herein. The present invention iscompatible with existing ABS control systems using existing algorithmsfor the conventional caliper system. Improved braking can be obtainedwith use of a new algorithm that utilizes the higher frequency and loweramplitude more efficiently than the algorithm developed for thisconventional, higher pressure, ABS controller. The finer resolution in asense reduces the “hunting” of the pressures about a center line oraverage line for the pressure changes shown in these graphs. Because ofthe finer resolution, it also may be desirable to increase the samplingrate, for example, by doubling the number of input elements around thewheel that are being sensed by a sensor, such as a Hall effect type ofsensor 11 a (FIGS. 1A and FIG. 1G) to provide double the number of inputsignals to the ECU. Further, the input signals may be further magnified,and the flat bottom of a current signal may be processed to give a finerresolution of pressure variation at the changeover from a decreasingpressure to an increasing pressure at the brake pads. This additionalinformation could be of use in the new algorithm.

[0054] In accordance with an important aspect of the invention, thereduction in pressure being used to generate the braking clamping forceover four clamping surfaces rather than two clamping forces allows theuse of a solenoid 110 (FIG. 1F) to operate the brakes rather than theconventional rotary electrical motors with gear trains to provide amechanical advantage. That is, as illustrated in FIGS. 1F and 18, asolenoid 110 or a pair of solenoids 110 and 112 may be used to providethe force for actuating the brakes at a force equivalent to 20 Bar orabout 10 Bar if a pair of hydraulic cylinders are provided in the stubaxles, as illustrated in FIG. 18.

[0055] From the date developed with the test vehicle, there was found tobe a reduction in pressure from about 70 BAR to 35-40 BAR for highcoefficient road surfaces. On low coefficient of friction road surfaces,such as ice, the conventional caliper system operated in a range of15-20 BAR of line pressure while the twin brake system operated at 6-10BAR of line pressure. The frequency was about double in each instance,and the amplitude of pressure variation was about halved. This is withthe use of a single cylinder 72 rather than a pair of cylinders, whichshould allow a further reduction by about one-half, if such a lowerpressure system is desired. These lower pressures are most useful forbrake-by-wire systems because this allows the use of the lower force,solenoids rather than the large force, complex, rotary motors and geartrains now used to provide a mechanical advantage in order to developthe high forces currently needed for the conventional caliper disc brakesystem.

[0056] The illustrated twin brake system shown in FIG. 1G will now bedescribed in detail and it comprises at least one pair of brake discs38, 40 which are mounted on a hub 14 of a suspension for a vehicle withthe braking disc being constrained i.e., positioned on the hub 14, alongits inner radial portion by a resilient radially directed forceapplicator 44 acting between the hub 14 and the brake disc and by anouter force applicator assembly 45 which is positioned at the outer rimof the disc. This construction provides a rotational geometry for thedisc to have contact between the disc and the brake pads in a randomnature, thereby resulting in a lower residual, off-brake torque andreduction of DTV. That is, a gentle random touching of the brake padsand brake disc may occur when driving straight ahead with the pads anddisc being held in non-tilting positions relative to one another. Theinner, radially directed, force applicator is positioned between theslidable disc, and the hub to provide friction forces to the hub and tothe disc which holds them against sliding relative to one another andagainst generating a noise or a high squeal when the brake disc isheated and expanded. That is, when the brake disc was cold, no squeal ornoise was generated at the spline interconnection. But, when the discwas heated and expanded, disc spline members or teeth 42 (FIG. 5) wereloose and slid in hub splines 20 and generated high pitched squealingnoises.

[0057] The preferred radial, inner force applicator 44 comprisessprings, preferably flat leaf springs 44 a, that are laid tangentiallyof the hub at their centers 44 b (FIGS. 4 and 5) and with their outerends 44 c biased into contact with inner hub surfaces at spaced points,as illustrated in exaggerated form in FIG. 4. More spaced points ofcontact can be provided by providing raised ribs 44 d on the leafsprings 44 x, as illustrated in FIGS. 13 and 14.

[0058] The slidable brake disc 38 is thus supported in a floating manneron points of contact 44 c (FIG. 4) with the leaf springs 44 a on the hubin a floating manner and the brake disc can be shifted axially withforces applied thereto to overcome the frictional forces being appliedby the springs at inner disc hub surface. When the brake disc expandsconsiderably due to a disc high temperature, the disc teeth become loosein the colder spline hubs and the frictional forces between the leafsprings 44 a and the brake disc and hub restrain the disc from shiftingrelative to the hub and a resultant squealing noise. The leaf springs 44a impart radially directed forces to the inner hub portion of the brakedisc to keep it generally in a plane normal to its rotational axisthrough the center of the hub. This inner radial positioning by thesprings 44 a assists in keeping the disc 38 concentric with therotational axis and within a relatively tight space envelope at thebrakes off condition thereby reducing rubbing contact between the brakepad's frictional surfaces and the brake discs 38, 40 and a resultantdisc thickness variation (DTV). DTV which is a major source ofvibration.

[0059] In accordance with an important aspect of the invention, slidablebrake discs 38 and 40 float on the hub 14 and its outer rim portion isconstrained to its off-brake position, and each disc seeks or floats toan off-brake position established by engagement with slidable brake pads50, 54 and 56, which slide on the guide surfaces 68 of the bridge-shapedguide member 64. As best seen in FIGS. 2, 3 and 3A, a brake pad, forceapplicator 71 is positioned to apply radially directed loads to theslidable brake pads to constrain them from sliding with predeterminedspring forces. The spring forces are much stronger than that neededmerely to prevent rattling or noise suppression. The spring forces aresufficient to restrain the slidable brake pads from moving into contactwith the brake discs in an uncontrolled manner. It has been found thatif only a light spring force is supplied to suppress noise, that thenoise will be abated; but that the brake pads are free to shift and rubagainst the brake discs causing wear and DTV. Also, when using verylight springs, the brake pads will not assist in positioning the outerrims of the slidable brake discs to reduce off-brake residual torque.The illustrated force applicator 71 comprises a pair of leaf springs 71a and 71 b (FIGS. 2 and 5) which form the dual functions of preventingrattle and positioning of the pads and discs relative to each other.

[0060] After the brake has been applied and released, the rotating brakedisc 38 initially rubs against the brake pads and forces from thisrubbing cause the disc pads 50 and 56 to slide in opposite directionsfrom the rotating disc. The amount of shifting is controlled by thebrake force applicator's frictional force being overcome. Conversely,the off-brake, residual torque position of the rotating brake disc 38 isbeing constrained by the forced-apart brake pads, which are being heldagainst further sliding by the force applicators. The force applicatorsprings 44 also are controlling any lateral sliding of the brake disc 38along the hub. The brake disc 38 is being constrained in its off-loadposition by the outer force applicators acting on opposite sides of thepair of discs and the inner springs 44 acting on the inner hub portionof the discs. Thus, the disc is controlled to be free to slide and floatbut not to topple into the brake pads and the brake pads have controlledsliding but are not free to topple or to be free to vibrate into or bangagainst the discs.

[0061] The ABS twin disc brake assembly 10 of the present invention,because of its floating geometry as described above, has a significantlylower drag torque, i.e., off-brake residual torque, as will be explainedin connection with FIG. 8 which illustrates a typical result for thedisc temperature curves from 100 Kph. for the ABS twin disc brake versusa conventional, ABS disc brake. The conventional fixed brake curves 13Aplateaus at best is 35° C. above ambient while the ABS twin disc brake10 continues to cool and stabilizes at 10° above ambient, as illustratedby the straight line 13B. Usually, the conventional brake was found tobe about 50°-70° C. above ambient. The assumption made with respect tothis test is that dynamic drag due to disc face contact with the pad isproportional to temperature at the disc. The present invention isdesigned to preferably produce a low residual torque, e.g., about 1newton meter or less in contrast to about 6 newton meter for the fixeddisc brake on the vehicle being tested herein.

[0062] As explained above, the vehicle wheel being used in this ABS twinbrake system can accelerate faster toward the vehicle speed because oflower residual torque drag than can the conventional ABS wheels havingthe high torque drag from the conventional disc brake.

[0063] In accordance with the invention, the brake discs 38 and 40 mustbe flat and planar in their rotational plane and substantially normal tothe rotational axis 9 (FIG. 2). The brake disc pads have outer planarsurfaces 50 a, 54 a; 56 a and 60 a which are held by the springs 71 aand 71 b to be parallel to the disc annular braking surfaces 38 a and 40a at the outer rim portion of the brake discs 38 and 40. When the discgeometry is slightly curved, i.e., not a flat planar surface, it hasbeen found that localized rubbing and wear occurred, as illustrated inFIG. 2, at a lower corner 50 b of the cylinder brake pads 50 and at theupper outer corner 54 b of the opposed brake pad 54 on the slidable padcarrier 58. FIG. 2 shows a very exaggerated tilted disc 38 in lines toillustrate the point being made. The non-flat brake disc did not haverandom contact with the brake discs 38 and 40; but had localized rubbingcontact due to the disc curvature at the inner and outer corners Sob and54 b during each or almost each revolution of the brake disc. Severedisc thickness variations resulted and vibrations of the brake occurred.When the non-flat discs were replaced with flat brake discs the randomengagement of the pads and discs was again achieved, the DTV andvibrations associated with the DTV were eliminated. If a localized spotcarries the load, you get wear and a pumping action at wheel frequency.

[0064] While not illustrated herein, it was found that if the slidablebrake pad surfaces 50 a, 54 a, and 56 a (FIG. 2) were not held inparallel relationship to the brake disc faces 38 a and 40 a, but werefreely mounted or loosely mounted on the bridge, that the brake padscould tilt or cock and cause DTV and resultant vibration, as describedabove for a non-flat brake disc. Stated differently, the springs 71 aand 71 b were strong enough to hold the brake pads against a tiltingthat would shift their planar pad surfaces 50 a, 54 a and 56 a fromplanes perpendicular to the rotational axis 9 and would bring a cornerthereof into continual, localized rubbing contact with a brake disc inthe off-brake position. Thus, the floating geometry for the brake discsand constraint of the brake pads and discs to achieve random contact atthe off-brake position is an important aspect of the invention.

[0065] AMS fade tests were run to compare the performance of the ABStwin disc brake assembly 10 of this invention versus the standardfactory equipped fixed brake disc, and the results are shown in FIGS. 9and 10. As seen in FIG. 9, there are ten peaks on the graph for each ofthe ten braking stops with the brakes cooling and showing a temperaturedrop of about 30° C. and a maximum disc temperature of about 700° C.which is the Judder range. In contrast, the ABS twin slidable brake discsystem had a maximum temperature of 580° C. (FIG. 10) or about 120° C.lower than the conventional disc brake. The temperature drop betweenbraking events was about 80° compared to only a 30° C. temperature dropfor conventional disc brake. Thus, the present ABS system passed the AMSfade test where the conventional ABS brake system being tested did notpass the AMS test.

[0066] In accordance with the present invention, the preferred driveconnection 19 has the brake disc teeth 42 sized to fit the grooves 20along both of the groove flanks 21 without using oversized grooves. Thisis in contrast to the prior art which used oversized spline grooves andsmall springs therein to engage the driving side flanks of the hub anddisc; but this prior art solution led to other problems like disc wobbleon the hub. Preferably, the driving connection of the present inventionis a very efficient one such as that akin to a pair of meshed gearswhere the contact is a line of contact across the engaged flanks 21(FIG. 15A) rather than a small point of contact to provide lower unitpressures. Preferably, this line of contact is maintained whether thebrake disc has a high or low temperature. The plastic deformation at theengaged spline surfaces keeps the engaged spline members clean fromcorrosion. The present invention eliminates the brinneling, dustgeneration, and squirming of the disc at high braking torque.

[0067] The hub 14 is an integral casting and, as is conventional, has ahollow cylindrical rearward projection 14 a which has a splinedinterior, and an exterior, which provides a mounting for roller bearings16 (FIG. 7). A splined projection of a constant velocity joint (notshown) at the end of a drive shaft is received within the projection sothat the hub can be rotated on the bearings 16 by the drive shaft. Thehub also has an annular disc-like portion 14 b from which the portionprojects rearwardly. The hub provides a mounting for the wheel (notshown) which is bolted against a forward surface of the portion by boltsreceived in holes 14 d. The hub also has a hollow cylindrical rearwardprojection 14 c of greater diameter than the portion. The portionprojects from the outer edge of the portion 14 b. The portion 14 c hasan outer surface provided with grooves 20 running parallel to the axis22 about which the hub rotates. The grooves 20 are arranged in fourequally circumferentially-spaced locations.

[0068] The suspension link 12 (FIG. 11) is an integral casting andcomprises a hollow cylindrical portion 12 a of conventional form, whichprovides a mounting for the bearings 16 so that the hub 14 rotates onthe link. The link also comprises top 24 and bottom 26 mountings forsupports of the link. The top mounting is provided by a portion 12 b ofthe link which projects rearwardly from a portion 12 c which projectsupwardly from the portion 12 a. The portion 12 b is of conventional formand forms two semi-cylindrical arms (FIG. 5) which together form a clampwhich can be tightened by a bolt (not shown) which extends through bores28 in the arms and across a gap between them. A McPherson strut (notshown) can be clamped between the arms of the portion 12 b so that thelink can pivot about the longitudinal axis of the strut.

[0069] The bottom mounting 26 is provided by a portion 12 d of the link12, which projects downwardly from the portion 12 a thereof. Thisportion 12 d is of conventional form and has a vertical bore 30, toreceive a pin of a ball joint (not shown), and two horizontal bores 32in which bolts (not shown) can be received to connect the link to a tiebar (not shown).

[0070] The link 12 also comprises an arm 34 for connection to a trackrod (not shown) of a steering system of the vehicle. This arm 34 is ofconventional form and is provided by a portion 12 e of the link 12,which projects sideways from the portion 12 a thereof. The arm 34comprises a vertical bore 36 through which the arm can be pivotallyconnected to the track rod. In order to steer the vehicle, the track rodis moved to cause the link to pivot on the joint 18 and the mountings 24and 26.

[0071] The twin discs 38 and 40 are identical to one another and aremounted for limited movement on the hub 14 in a direction generallyparallel to the axis 22 about which the hub rotates. Specifically, eachdisc is in the form of a flat annular plate and has inwardly-projectingteeth 42. As best seen in FIGS. 5, 15 and 15A, it is preferred that thebrake discs 38 and 40 each have a limited number of wide teeth, i.e.,the illustrated four teeth 42 that mesh with the spline grooves 20 a ofsplines 20 on the hub. The spline grooves 20 a are four in number, inthis instance, and have flanking walls 21 (FIG. 15) that match flankingwalls 42 a on brake disc teeth 42. The engaged flanks 21 and 42 a havean angle A for their respective tooth flange angles. Manifestly, thenumber of teeth and splines may be varied. Because of large stressesgenerated on the thin teeth 42 on these relatively thin brake discs,there is a tendency of stress cracks to form, particularly after hightemperature heating and cooling cycles and high stress cycles. Torelieve such stress, there are provided large, curved, stress relieffillets or cut-outs 42 b in the respective brake discs. Herein, as shownin FIGS. 15 and 15A, the stress relieving fillets are provided on eachside of a tooth 42 and provide generally semi-cylindrical,cross-sectional openings on each side of each tooth, when the teeth arefitted into a spline grooves, as shown in FIG. 15A.

[0072] As best seen in FIG. 5, the four grooves 20 on the hub arerelatively small compared to the projecting teeth 20 b defined betweeneach pair of adjacent grooves 20. These teeth 20 b on the hub havelarge, arcuate surfaces 20 c against which are laid the leaf springs 44.Thus, each leaf spring 44 has a large circumferential area contact withinner, arcuate surfaces 42 c of the brake disc in the place betweendepending teeth 42 thereon.

[0073] Four leaf springs 44 are mounted on the hub 14 to provideresilient force applying means to apply radial forces between the huband the discs 38 and 40. These radial forces prevent the discs fromtilting on the hub, prevent rattling and control sliding of the discsalong the hub. The resilience of the springs allows thermal expansion tobe accommodated, as explained above. The springs are secured in asuitable manner, such as by screws 46 to the outer surface 20 c of thehub portion 14 c in the gaps between the spline grooves 20 a. Each ofthe four springs engages both of the discs 38 and 40 in the areasbetween the teeth 42, giving a resilient four-point mounting for eachdisc. The discs can slide on the hub parallel to the axis 22 with theteeth sliding in the spline grooves 20 a.

[0074] As best seen in FIG. 4, the flat leaf spring 44 is engaged withand has a pressure line of contact with the hub at point 44 b; and theouter ends of the spring 44 c have been flexed downwardly to providepressure line of contact engagement with the discs 38 and 40 at thesebent spring ends. In order to provide more lines of engagement betweenthe disc and the hub, the spring 44 x may be provided with ribs 44 dtherein, as shown in FIGS. 13 and 14. Also, it is preferred to separatethe spring 44 into separate biasing portions 44 h and 44 i (FIG. 13)separated by a slot 44 j each portion acting on an associated disc 38 or40 to provide more individualized, independent pressure forces betweenthe associated disc and the hub. The springs 44 are balanced in theforce they apply to the brake discs 38 and 40 relative to the forcewhich the springs 71 a and 71 b apply to the slidable brake pad carriers52 and 58. Both the brake discs and the brake carriers are constrainedagainst shifting along the hub and the bridge respectively, due tovibrations and inertial forces from the vehicle when it is traveling.Thus, it will be seen that the springs 44 allow the slidable brake discsto: float on the hub, hold the discs in a radial plane normal to therotational axis, apply frictional forces that prevent squealing; applyfrictional forces that aid in holding the discs in position whilerotating in their off-brake positions; and permit axial forces from theforce actuator to outwardly slide the discs to their braking positionwith engagement of the disc 40 with the stationary brake pad 60.

[0075] Turning now in greater detail to the illustrated brake pads,these pads comprise the first pad 50 which is mounted on a backing plate52 and is arranged to engage a side surface of the disc 38, pads 54 and56, which are mounted on opposite sides of a backing plate 58 and arearranged, respectively, to engage the opposite side surface of the disc38 and a facing side surface of the disc 40, and the pad 60 which ismounted on a backing plate 62 and is arranged to engage the oppositeside surface of the disc 40. The backing plate is fixedly mounted on aguide member or bridge 64, which is, in turn, fixedly mounted on theportion 12 c of the link 12. Specifically, two bolts 66 pass throughbores through the portion 12 c and the guide member 64, and havethreaded ends which are received in threaded bores in the backing plate.The stationary guide member 64 provides two guidance surfaces 68 onwhich the backing plates 52 and 58 slide. The guidance surfaces 68extend, parallel to the axis 22, along opposite sides of the member 64.The guidance surfaces may take other forms such as the shafts of thebolts 66.

[0076] Each guidance surface 68 receives a pair of concave, U-shapedprojection or hooks of the pad carriers 52 and 58. As best seen in FIG.3A, the slidable pad carrier 58 has hook-shaped projections 59 withinner sliding surfaces 59 a, which are slidably supported on theupwardly-facing support surfaces 68 of the bridge 64. To assist inachieving the desired balance to allow the brake pad carriers 52 and 58to be pushed apart from and by the brake discs 38 and 40, when they areshifting axially from their brakes-on to their brakes-off positions; andyet constrain the pad carriers and their brake pads from tilting, it ispreferred to machine flat the inner sliding surfaces 59 a on thecarriers and the supporting surfaces 68 on the bridge. Flat machinedsurfaces on the carriers engaging flat machine surfaces on the bridgeassures a more uniform, frictional, constraining force to retain thebrake pad carriers against axial sliding from their off-brake positions.Also, the carriers will have broader, wider engagement with bridgesupporting surfaces 68 to assist in preventing significant rocking ortilting on the bridge under vehicle inertial forces and/or vibrationswhen the vehicle is moving, as would cause localized rubbing contact inthe off-brake condition.

[0077] If the slidable brake pad position is not controlled, theslidable brake pad may tilt to engage or to vibrate against the slidablebrake disc and generate a random wear pattern on the disc causing DTVand vibration of the disc. The control of the slidable pad and disc isimportant in a very dynamic situation with the vehicle wheel carryingthe slidable brake system over bumpy or smooth roads, cornering withbrakes on, cornering with brakes off, with ABS system on, with an ABSsystem off, etc. On cornering, the hub deflects and moves the discsurface to engage the brake pad; and after cornering, the pad and discseparate as the brake recovers to its steady state of low residualtorque at the off-brake position. In the embodiment of the invention,illustrated in FIGS. 2, 3 and 3A, the preferred force applicatorscomprise flat leaf springs 71 a and 71 b that have been bent from theirflat planar condition to a bow configuration in which outer edges 71 cand 71 d of the springs abut top end surfaces 52 a, 52 b, 58 a, 58 b ofthe respective slidable brake carriers 52 and 58. The center portion ofthe leaf spring 71 a is secured by a suitable fastener, such as screws69 threaded through the spring and into the stationary bridge 64 at acentral location on the top of the stationary bridge 64.

[0078] The force applicator 71 may take many forms, and it is hereinillustrated in FIG. 3 as having the two separate leaf spring portions 71a and 71 b, each of which is separately applied resilient, biasingforces to its associated brake pad holder 52 or 58. The leaf springportions 71 a and 71 b are preferably connected by a short integral,central web 71 f, which is located between a pair of facing, elongatedslots 77 dividing the spring leaf into the two discrete spring forceapplicator sections. Thus, if one brake pad holder has high pointsthereon or other force mitigating or amplifying factors affecting it andits associated spring; the other brake pad holder and its associatedspring should be isolated therefrom.

[0079] As previously explained in the embodiment of FIGS. 1-17, thebrake actuating force used to brake the vehicle is from a brake actuatorwhich is in the form of a hydraulic piston and cylinder assembly 75. Inthe embodiment of the invention described in connection with FIG. 18, asan alternative to the use of an electric motor and a gear drive used inthe prior art, brake-by-wire ABS systems, the solenoid 110 (FIG. 1F) orpair of solenoids 110 and 112 (FIG. 18) may shift the movable brake padcarriers 52 and 58 to carry the slidable brake pads into theirrespective braking positions and slide the brake discs axially along thehub 14 into their respective braking positions.

[0080] The illustrative force actuator system comprises a piston andcylinder assembly operable to urge the pads 50, 54, 56 and 60 intoengagement with opposite side surfaces of the discs 38 and 40 to brakethe hub 14 and hence, the wheel. The piston and cylinder assemblycomprises a cylinder 72 which is defined by the portion 12 c of the link12. Thus, the cylinder is formed integrally with the remainder of thelink. A brake-bywire actuator such as the solenoid 110 shown in FIG. 1For an electric motor (not shown) may be mounted in the hollow cylinderbore 72 rather than the piston 74. Herein, the piston 74 of the assemblyprojects from the cylinder and engages the backing plate 52 on theopposite side thereof to the pad 50. The piston and cylinder assembly isoperated by supplying hydraulic fluid under pressure to a bore 76 in thelink portion 12 c which communicates with the cylinder. Herein, thehydraulic pressure for operating the twin disc brake system was about 30to 35 BAR which is one-half of the 70 BAR pressure of the conventionalfixed disc brake on the other test vehicle. The piston had a face ofabout 200 mm in area. The piston moves out of the cylinder moving thebacking plates 52 and 58 and the discs 38 and 40 until the disc 40engages the pad 60, which does not move.

[0081] The hydraulic piston and cylinder assembly 75 includes a sealwhich acts between the cylinder 72 and the piston 74 to prevent egressof hydraulic fluid from the cylinder. This seal is provided by anelastomeric sealing ring, which is mounted in an annular groove formedin a cylinder wall, the ring projecting from the groove to engage thepiston. This sealing ring also serves as an energy storing mechanism.Specifically, when the assembly is operated to move the piston outwardlyof the cylinder to put the brake “on”, the ring is compressed therebystoring energy therein. When the pressure of the hydraulic fluid in thecylinder is reduced, the ring releases the stored energy therein bymoving the piston inwardly of the cylinder (away from the brake disc).Accordingly, the sealing ring has to engage the piston with asignificant force. Movement of the piston away from the disc allows themovable pads 50, 54 and 56 of the brake to be moved away from the discby forces exerted thereon by the rotating slidable brake discs 38 and 40overcoming the force of the spring 71 a and 71 b; thereby putting thebrake into a “brakes-off” condition.

[0082] The return of the piston 74 by the seal reduces the off-braketorque because there is no significant force being applied by the pistonto the brake carrier 52 and its brake shoe 50 relative to the facingside of the slidable brake disc 38. Conversely, the floating brake discs38 and 40 are constrained and float on the hub 14 and will not shift thepiston inwardly into the cylinder to displace hydraulic fluid, in thecylinder causing “knock-back” during cornering or other dynamicmovements of the wheel assembly. The reduction of knock-back provides abetter feel to applying the brakes with less fluid displacement, andeliminates the occasional long pedal displacement feel where substantialfall-back has occurred.

[0083] From the foregoing, it will be seen that the present inventionprovides a much smaller disc brake assembly without the very largecaliper sliding and bolts as in the conventional, fixed disc brake. Thecaliper is large because it carries the cylinder and piston and theslidable bridge must withstand and transfer the large torque brakeloads. The present invention is smaller because the cylinder can beintegrated with the support and the bridge does not slide and carry thepiston. Because of knock back and other problems, this large fixed brakeis usually mounted at about 3:00 or 9:00 o'clock positions whereas inthe present invention the brake is mounted at the top of the unit at the12:00 o'clock position. The stiffness problem of the bridge with itsdeflection, e.g., 0.006 inch, is reduced by a factor of four when usingfour brake pads and one-half the hydraulic line pressure allowing asmaller and lighter weight brake assembly. The time of mounting andassembly of the brake, as well as repair or replacement, is enhancedbecause of the front bolting and the telescopic sliding of the brakediscs and of the brake components versus the bolt from the rear orbehind of the fixed brake bolts on which the caliper slides.

[0084] As explained above, the ABS twin brake system of this inventionoperates at about one-half of fluid pressure of the conventional ABS forthe same vehicle. If it is desired to reduce the pressure again by aboutone-half, a pair of hydraulic cylinders 102 (FIG. 12) may be used ratherthan a single cylinder within the stub axle. Alternatively, a pair ofsolenoids 110 and/or 110, 112 (FIG. 18) could be housed in bores in thestub axle rather than a single solenoid to reduce the force needed andto supply redundancy of operation if one solenoid should fail. The brakecylinder of FIG. 16 and the pair of brake cylinders of FIG. 12 for theactuator system 100 of FIG. 12 have like parts which are given the samereference numerals and are not further described. The assembly 100 hastwo parallel cylinders 102 formed in portion 12 c of the stub axle. Inthis case, each of the cylinders 102 has a smaller transversecross-sectional area than the cylinder 72, but the total area of thecylinders 102 is greater. Each of the cylinders 102 has a piston 104therein and the pistons 104 cooperate in pressing the backing plate 52.In order to accommodate the two piston and cylinder assemblies, theguide member 64 is modified to arch over the pistons, as shown at 106and the bolts 66 are replaced by three bolts 108. The use of two pistonand cylinder assemblies enables greater force to be applied for the samepressure in the cylinders (or the same force to be applied for lowerpressure) and this force can, on average, be applied at a greaterdistance from the axis 22. If desired, the two cylinders can be ofdifferent diameters, e.g., with the leading cylinder in the normaldirection of rotation, being of greater diameter.

[0085] In the illustrated embodiment of the invention described herein,the force actuator for the applying of the brake clamping pressure hasbeen from the conventional vehicles hydraulic system having a commonmaster cylinder and hydraulic lines or hoses extending from the mastercylinder to four cylinders, such as the illustrated two, front wheelcylinders, the rear wheel cylinders for operating the rear drum brakes,have not been illustrated herein.

[0086] In accordance with a further embodiment of the inventionillustrated in FIG. 1E, a master cylinder 13 a (FIG. 1A) and its lines13 b have been eliminated and each stub axle of the suspension, oranother part of the suspension, is provided with its own localizedcaliper unit having its localized hydraulics. More specifically, thestub axle or suspension 200 is provided with a small reservoir or hollowportion 202 in a stub axle with a fluid connection, such as a bore hole204 in the stub axle leading to the hydraulic cylinder 72 to operate thepiston to slide the slidable brake pads 50, 54 and 56 to force the outerbrake disc into clamping engagement with the outer, fixed brake pad, asdescribed above.

[0087] To maintain the desired hydraulic pressure in the small cylinder200 on the suspension 200, a pressure generator device 206 (FIG. #) ismounted on and attached to the reservoir, and the energy used toincrease the hydraulic pressure in the reservoir is derived from themass of the vehicle as it bounces up and down. More specifically, thedampening system for the vehicle wheel including shock absorbers or thelike are used to actuate a pressure generator device. For instance, aplunger 210 is mounted to be pushed by the vehicle mass to move adiaphragm 212 in the reservoir 202 to increase the pressure to thedesired constant pressure, e.g., 20 BAR. Currently, there are air ridesor cushions in vehicles that use the mass of the vehicle to increase airpressure in these kinds of dampening systems and similar devices may beused as a pressure generator for the hydraulic fluid in the reservoir202.

[0088] To provide the ABS control for the ABS Braking System 200preferably includes its own ABS controller, such as in the form of acomputer chip 214 or the like, mounted on the stub axle along with apressure control or modulating valve unit 215. Additionally, a smallcontrol valve 216 for the ABS controller is provided on the suspensionof each wheel to control the hydraulic pressure and actuation of thepiston in the cylinder 72 to decelerate the wheel and to releasehydraulic pressure to allow the wheel to accelerate toward the vehiclevelocity. The preferred, hydraulic, control valve unit 215 has amodulating valve including a plunger 217 operating in a fluid filledchamber 218 and by sliding the plunger forwardly to reduce the volume inthe chamber 218 the pressure is increased in the cylinder 72.Conversely, by pulling the plunger 217 rearwardly the volume in thechamber is increased and the hydraulic pressure in the brake cylinder 72is reduced. The plunger 217 is shifted either in predeterminedincrements of travel or in infinite travel amounts by a solenoid 220having a solenoid rod 221 for reciprocating in the solenoid case. Thesolenoid rod 221 has one end attached to the plunger. The solenoid isoperated by the ABS controller 214. In contrast to the conventionalsystem having a modulating valve 17 (FIG. 1), the modulating valve 215sees a positive pressure from the reservoir rather than stopping fluidinflow through a check valve connected to the master cylinder.

What is claimed is:
 1. A vehicle wheel brake system for a wheelsuspension assembly and having an anti-lock braking system (“ABS”) toprovide a higher resolution brake apply and brake release relative to anABS system having a single, fixed brake disc, the brake systemcomprising: a mounting hub for a road wheel mounted on the wheelsuspension assembly for rotation about a rotational axis; at least twoslidable brake discs mounted to slide axially along the hub betweenbraking and off-brake positions; a caliper including a fixed bridge andat least four (4) braking pads mounted on the fixed bridge to providefour braking surfaces for braking engagement with the opposing sides ofeach of the brake discs; a pulse creator mounted on the hub forgenerating pulses; a sensor mounted on the wheel suspension assembly forsensing pulses from the pulse creator and for providing signals withrespect to the rotational condition of the road wheel; an ABS controllerconnected to the sensor and providing signals when the wheel conditionis within preset parameters relative to the speed of the vehicle todevelop a theoretical deceleration curve for the stopping of the vehiclewithin a predetermined distance; and a brake actuator system operablemanually by the vehicle passenger and operable automatically by the ABScontroller to operate the caliper to slide the brake discs axially andto cause application of the four brake pads at a pressure of aboutone-half or less of the pressure of operation of the fixed, brake discsystem and a frequency of brake apply and release of at least double thefrequency of brake apply and release of the fixed, brake disc system. 2.A vehicle wheel system in accordance with claim 1 wherein a hollow boreis formed in the suspension member to reduce the weight of thesuspension member and to contain the force applicator at a locationcloser to a wheel-turning axis to allow a reduction in turning radius.3. A vehicle wheel ABS braking system in accordance with claim 1, havingreduced residual torque drag, comprising: springs between the hub andinner portions of the slidable brake discs to mount the brake discs in afloating manner on the hubs; and springs on the fixed caliper forholding the brake pads in position relative to the brake pads duringvehicle wheel speed-up.
 4. A vehicle wheel ABS braking system inaccordance with claim 1 having reduced weight and reduced residual dragtorque, comprising: a hollow, cylindrical bore formed in the suspensionmember having a force actuator contained therein; springs floating andsupporting the slidable brake discs on the hub; and springs on thecaliper for engaging the slidable brake pads and for holding them inposition relative to the slidable brake discs in the off-brake positionto reduce residual torque drag therebetween.
 5. A vehicle wheel brakingsystem, in accordance with claim 1, wherein the brake actuator systemcomprises: an integral, hydraulic cylinder for holding a hydraulic fluidintegrally formed in a suspension member of the wheel suspension; and apiston mounted in the integral hydraulic cylinder and is operable by thehydraulic system to engage the four brake pads with the two axially,slidable brake discs.
 6. A vehicle wheel ABS braking system, inaccordance with claim 1, wherein the brake pad actuator comprises asolenoid and an electrical system for selectively energizing andde-energizing the solenoid.
 7. A vehicle wheel ABS braking system, inaccordance with claim 1, wherein the brake actuator comprises: ahydraulic system having a hydraulic cylinder at each wheel; a hydraulicreservoir for containing hydraulic fluid at each of the ABS-controlledbrake pads to supply hydraulic fluid to an adjacent, hydraulic cylinder;and a pressure generator at each wheel suspension operable by the massof the vehicle for pressuring the hydraulic fluid in each hydraulicreservoir.
 8. A vehicle wheel ABS braking system, in accordance withclaim 1, wherein the pulse generator comprises a ring of spacedgenerator elements mounted on a side of the rotatable hub; and thesensor comprises a magnetic sensor disposed on the suspension memberclosely adjacent the ring of spaced generator elements.
 9. A vehiclewheel ABS braking system, in accordance with claim 1, wherein thecaliper is mounted on the suspension member in a vertical plane throughthe rotational axis and above the rotational axis and a radially outerposition relative to the rotational axis; and the pulse generator andthe sensor are located radially inwardly of the caliper.
 10. A vehicledisc brake and suspension system having an ABS system comprising: awheel suspension member having a hub and connections to other portionsof the vehicle steering device; at least two brake discs each having aninner portion slidably mounted on the hub for sliding in a directionparallel to the central axis of the hub between a braking position andoff-brake position; at least four braking pads including one outer,fixed, brake pad and at least three slidable brake pads each having afriction pad surface for applying braking torque to opposite sides ofthe brake disc when in the braking torque position to decelerate theengaged brake discs; a hollow bore in the suspension member; an actuatorin the hollow bore of the suspension member for sliding the slidablebrake pads and brake discs into the braking position; force applicatorsfor floating the brake discs to allow them to slide axially from abraking position to an off-braking position relative to the brakingpads; an outer rim portion on the braking disc rotating while in theoff-brake position and engaging the slidable brake pad's frictionsurface to slide the pad from the braking position to an off-brake padposition; a caliper fixed to the suspension member and having slidablebrake pads thereon operable by the actuator into braking engagement withthe slidable brake discs; a brake pad force applicator acting on theslidable brake pads, when its off-brake position, to constrain thefriction pad surfaces engaging the brake disc to reduce tilting of thebrake pads on the stationary support and its rubbing on the brake discsthat would increase off-brake, residual torque; and an ABS system foroperating the brake pad force applicator within the hollow bore in thesuspension member to slide the brake pads and brake discs iteratively tothe braking position and releasing the brake pads and discs to slide tooff-brake positions.
 11. A vehicle ABS brake system, in accordance withclaim 10, wherein the actuator for sliding the brake pads comprises ahydraulic cylinder and a piston in the cylinder for applying the brakepads at 40 BAR or less when the vehicle is on a high coefficient offriction road surface.
 12. A vehicle ABS system, in accordance withclaim 10, wherein the actuator for sliding the brake pads comprises asolenoid and an electrical system to operate the solenoid.
 13. Thevehicle ABS braking system, in accordance with claim 10, wherein thebrake pad force applicator acts on the slidable brake pads, when thesystem is in an off-brake position to constrain the friction padsurfaces from engaging the brake discs and to reduce tilting of thebrake pads and rubbing on the brake discs that increases off-brake,residual torque.
 14. A disc brake system, in accordance with claim 13,wherein the brake pad force applicator applies force to each slidablebrake pad to hold its face in a plane substantially parallel to theplane in which the disc is rotating to minimize tilting of the brake padinto engagement with the brake discs, which would cause disc thicknessvariation.
 15. A disc brake system, in accordance with claim 14, whereinthe brake pad force applicator comprises at least one spring pushing onthe brake pads in a direction substantially normal to the rotationalaxis of the brake discs and normal to the path of travel of the brakepads along a stationary support.
 16. A disc brake system, in accordancewith claim 10, wherein a stationary support comprises a bridge; theslidable brake pad comprises a slidable pad carrier mounted for slidingon the bridge and carrying the frictional pad surface thereon; and thebrake pad force applicator is positioned over the brake pad carrier andforces the brake pad carrier downwardly against the bridge.
 17. Avehicle wheel suspension system having an ABS braking system comprising:a suspension member; at least one brake disc mounted on the suspensionmember for rotation with a wheel of the vehicle; brake pads mounted onthe suspension member for movement to a brake application position toengage the at least one brake disc to decelerate the wheel and formovement to a brake release position to allow the wheel to accelerateduring an ABS braking operation; a hydraulic system at each of aplurality of wheels for shifting the brake pads to the brake applicationposition and for allowing the brake pads to shift to the brake releaseposition; a hydraulic reservoir mounted on the suspension at each wheelfor containing hydraulic fluid; a pressure generator at each wheelsuspension for an associated hydraulic reservoir operable by the vehiclemass movement to increase pressure in the reservoir; and an ABS controlsystem for operating the hydraulic system to iteratively shift the brakepads into the brake application position with vehicle wheel accelerationwith intervals therebetween of wheel acceleration to stop the vehicle.18. A vehicle suspension and ABS braking system, in accordance withclaim 17, wherein the at least one brake disc comprises a pair of brakediscs slidable mounted on the hub; and wherein four brake pads aremounted on the suspension member to engage four faces of the pair ofbrake discs.
 19. A vehicle suspension and ABS braking system, inaccordance with claim 17, wherein the hydraulic system comprises: anintegral, hollow cylinder formed in a stub axle suspension member; and apiston mounted in the integral, hollow cylinder.
 20. A vehiclesuspension and ABS braking system, in accordance with claim 17, whereinthe ABS control system comprises an intelligent control located at eachwheel for controlling that wheels iterative brake application and brakerelease.
 21. A method of braking a vehicle wheel using an ABS systemhaving an ABS hydraulic system and an ABS controller, and a wheel brakehaving a caliper and at least two of slidable brake discs axiallyslidable on a rotatable wheel supporting hub and having at least fourbrake pads engageable with the brake discs, the method comprising:operating the caliper to a braking position using 40 BAR or less ofhydraulic fluid pressure to slide the brake pads and the slidable brakediscs to a braking position; releasing the hydraulic fluid to allow theslidable brake discs to slide axially on the hub and to engage theslidable friction pads and to push them to their off-brake positions;floating the brake discs and the brake pads on their respective supportsin the off-brake position to reduce off-brake frictional drag andtilting of this brake pads against the brake discs; sensing operation ofa brake pedal by the operator generating an excessive braking force andsensing wheel speed and an approaching lock up of the road wheel usingan ABS controller; activating the ABS hydraulic system by the ABScontroller to shift the slidable brake pads on the fixed caliper withhydraulic pressure at 40 BAR or less; and shifting slidable brake padsand slidable brake discs on their floating supports rapidly to thebraking position with changes in pressure from 40 BAR and at apredetermined frequency in accordance with a stored algorithm in the ABSsystem.
 22. A method of braking, in accordance with claim 21, includinga reduction of weight of the system by forming a hollow, cylinderactuator bore in the suspension.
 23. A method of braking, in accordancewith claim 21, including positioning the caliper at about a 12:00o'clock position and above the rotating hub.
 24. A method, in accordancewith claim 21, including operating the piston within an integralcylinder at the top of the suspension member.
 25. A method, inaccordance with claim 21, including operating the caliper by the ABScontroller in the ABS mode at 40 BAR or less pressure on a high,coefficient of friction road surface and at a substantially higherfrequency than a system operating at about 70 BAR or more pressure onthe same high coefficient of friction road surface.
 26. A method, inaccordance with claim 25, including the step of operating the brake padsto engage and release the brake discs within the range of 8-20 Hertz fora low, coefficient of friction road surface.